1. Field of the Invention
The present invention relates to a motor control device and an electric steering system.
Priority is claimed on Japanese Patent Application No. 2008-139802, filed on May 28, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
Conventionally, for example, in electric power steering systems using the driving force of brushless motors, there are known systems which detect a rotation angle of a brushless motor by using a resolver and which, on the basis of the detection result, control the driving of the brushless motor (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2005-274484).
However, in the electric power steering system disclosed in Japanese Unexamined Patent Application, First Publication No. 2005-274484, when abnormal condition occurs in a rotation sensor, such as a resolver or an encoder, for directly detecting the rotation angle, it becomes difficult to flow a current with an appropriate phase to the brushless motor. Hence, it becomes difficult to perform the driving control. For this reason, in the case where an abnormal condition of the rotation sensor is detected, the driving control of the brushless motor is stopped, it becomes difficult to reduce the load of steering force which is necessary for a driver, and thus a problem arises in that the steering feels uncomfortable to the driver.